Nutrition, Metabolism, and Body Temperature Regulation

Dr. Gary Mumaugh

• Nutrient – a substance that promotes normal

growth, maintenance, and repair

• Major nutrients – carbohydrates, lipids, and

proteins

• Other nutrients – vitamins and minerals (and

technically speaking, water)

Nutrition

2

Nutrition

Figure 24.1 3

4

Food Pyramid System: Guiding

Principles

Overall

Health

Up-to-Date

Research

Total

Diet

Useful Realistic

Flexible Practical

Evolutionary

5

MyPyramid was

designed to help

people make

food choices for

meeting nutrient

requirements

Foods are

grouped

according to

nutrient content

6 .

Food Pyramid System Message:

Physical Activity

In the Dietary Guidelines:

• Engage in regular physical activity and reduce sedentary activities to promote health, psychological well-being, and

a healthy body weight

In MyPyramid graphic:

• Steps and person on them symbolize physical activity should be a part of everyday healthy living

7 .

Food Pyramid System Message:

Proportionality

In the Dietary Guidelines:

• Adopt a balanced eating pattern

– Sufficient amount of fruits and vegetables

– 3 or more ounce equivalents of whole-grain products per day

– 3 cup equivalents per day of fat-free or low-fat milk or milk products

In MyPyramid graphic:

• Differing widths of the color bands

suggest about how much

food should be eaten from

each group

8

Food Pyramid System

Message: Moderation In the Dietary Guidelines:

• Limit intake of saturated and trans fats, and choose products low in these fats

• Make choices of meat, poultry, dry beans, and milk products that are lean, low fat, or fat free

• Choose and prepare foods and beverages with little added sugars or calorie sweeteners

In MyPyramid graphic:

• Food group bands narrow from

bottom to top suggesting to eat

nutrient-dense forms of foods

9

1. Start with exercise

2. Focus on food, not grams

3. Go with plants

• Eat a plant-based diet

4. Cut way back on American

staples, e.g., red meat and

refined sugars and grains

5. Take a multivitamin and

maybe have a drink

• Complex carbohydrates (starches) are found in bread, cereal, flour, pasta, nuts, and potatoes

• Simple carbohydrates (sugars) are found in soft drinks, candy, fruit, and ice cream

• Glucose is the molecule ultimately used by body cells to make ATP

• Neurons and RBCs rely almost entirely upon glucose to supply their energy needs

• Excess glucose is converted to glycogen or fat and stored

Carbohydrates

12

• The minimum amount of carbohydrates needed to

maintain adequate blood glucose levels is 100 grams per

day

• Starchy foods and milk have nutrients such as vitamins

and minerals in addition to complex carbohydrates

• Refined carbohydrate foods (candy and soft drinks)

provide energy sources only and are referred to as

“empty calories”

Carbohydrates

13

• Fatty deposits in adipose tissue provide:

– A protective cushion around body organs

– An insulating layer beneath the skin

– An easy-to-store concentrated source of

energy

Lipids

14

• The most abundant dietary lipids, triglycerides, are found in both animal and plant foods

• Essential fatty acids – found in most vegetables, must be ingested

• Dietary fats:

– Help the body to absorb vitamins

– Are a component of myelin sheaths and all cell membranes

Lipids

15

• Higher for infants and children than for adults

• The American Heart Association suggests that:

– Fats should represent less than 30% of one’s

total caloric intake

– Saturated fats should be limited to 10% or

less of one’s total fat intake

– Daily cholesterol intake should not exceed

200 mg

Lipids: Dietary Requirements

16

• Complete proteins that meet all the body’s amino acid

needs are found in eggs, milk, milk products, meat, and

fish

• Incomplete proteins are found in legumes, nuts, seeds,

grains, and vegetables

• Proteins supply:

– Essential amino acids, the building blocks for

nonessential amino acids

• Daily intake should be approximately 0.8g/kg of body

weight

Proteins

17

• Proteins supply:

– Essential amino acids, the building blocks for

nonessential amino acids

• Daily intake should be approximately 0.8g/kg of

body weight

Proteins

18

Organic compounds needed for growth and good health

They are crucial in helping the body use nutrients and often function as coenzymes

Only vitamins D, K, and B are synthesized in the body; all others must be ingested

Water-soluble vitamins (B-complex and C) are absorbed in the gastrointestinal tract

Fat-soluble vitamins (A, D, E, and K) bind to ingested

lipids and are absorbed with their digestion products

Vitamins A, C, and E also act in an antioxidant

Vitamins

19

• Seven minerals are required in moderate amounts

– Calcium, phosphorus, potassium, sulfur, sodium,

chloride, and magnesium

• Dozens are required in trace amounts

• Minerals work with nutrients to ensure proper body

functioning

• Calcium, phosphorus, and magnesium salts harden

bone

Minerals

20

• Metabolism – all chemical reactions necessary

to maintain life

• Cellular respiration – food fuels are broken down

within cells and some of the energy is captured

to produce ATP

– Anabolic reactions – synthesis of larger

molecules from smaller ones

– Catabolic reactions – hydrolysis of complex

structures into simpler ones

Metabolism

21

• Energy-containing nutrients are processed in three major stages

– Digestion – breakdown of food; nutrients are transported to tissues

– Anabolism and formation of catabolic intermediates

– Oxidative breakdown – nutrients are catabolized to carbon dioxide, water, and ATP

Stages of Metabolism

22

• The process of forming sugar from

noncarbohydrate molecules

• Takes place mainly in the liver

• Protects the body, especially the brain, from the

damaging effects of hypoglycemia by ensuring

ATP synthesis can continue

Gluconeogenesis

23

• Most products of fat metabolism are transported in lymph

• Lipids are hydrolyzed by plasma enzymes and absorbed

by cells

• Only neutral fats are routinely oxidized for energy

• Catabolism of fats involves two separate pathways

– Glycerol pathway

– Fatty acids pathway

Lipid Metabolism

24

• Excess dietary protein results in amino acids

being:

– Oxidized for energy

– Converted into fat for storage

Protein Metabolism

25

• Amino acids are the most important anabolic

nutrients, and they form:

– All protein structures

– The bulk of the body’s functional molecules

Synthesis of Proteins

26

• Amounts and types of proteins:

– Are hormonally controlled

– Reflect each life cycle stage

• A complete set of amino acids is necessary for

protein synthesis

– All essential amino acids must be provided in

the diet

Synthesis of Proteins

27

Carbohydrate Metabolic Reactions

Table 24.2.1 28

Lipid and Protein Metabolic Reactions

Table 24.2.2 29

• The body exists in a dynamic catabolic-anabolic

state

• Organic molecules (except DNA) are

continuously broken down and rebuilt

• The body’s total supply of nutrients constitutes

its nutrient pool

State of the Body

30

• Metabolic controls equalize blood concentrations of

nutrients between two states

• Absorptive

– The time during and shortly after nutrient intake

• Postabsorptive

– The time when the GI tract is empty

– Energy sources are supplied by the breakdown of

body reserves

Absoprtive and Postabsorptive States

31

• Insulin controls the absorptive state and its secretion is

stimulated by:

– Increased blood glucose

– Elevated amino acid levels in the blood

– Gastrin, CCK, and secretin

• Insulin enhances:

– Active transport of amino acids into tissue cells

– Facilitated diffusion of glucose into tissue

Insulin Effects on Metabolism

32

• A consequence of inadequate insulin production

or abnormal insulin receptors

• Glucose becomes unavailable to most body cells

• Metabolic acidosis, protein wasting, and weight

loss result as fats and tissue proteins are used

for energy

Diabetes Mellitus

33

Is the structural basis of bile salts, steroid hormones,

and vitamin D

Is transported to and from tissues via lipoproteins

Lipoproteins are classified as:

◦ HDLs – high-density lipoproteins have more protein

content

◦ LDLs – low-density lipoproteins have a considerable

cholesterol component

◦ VLDLs – very low density lipoproteins are mostly

triglycerides

Cholesterol

34

• Because triglycerides and cholesterol are insoluble in

water, they do not circulate freely in the blood

• Instead, they are transported to and from tissue cells

bound to small lipid-protein complexes called lipoproteins

• High levels of HDL are thought to protect against heart

attack

• High levels of LDL increase the risk of heart attack

Cholesterol Transport

35

• Scavenge cholesterol from the bloodstream, from the

arterial walls and transports it back to the liver for

breakdown

• Think of HDL as the garbage trucks of the circulatory

system

A brief summary of liver functions

◦ Packages fatty acids to be stored and transported

◦ Synthesizes plasma proteins

◦ Forms nonessential amino acids

◦ Converts ammonia to urea

◦ Stores glucose as glycogen, and regulates blood glucose homeostasis

◦ Stores vitamins, conserves iron, degrades hormones, and detoxifies substances

◦ Hepatocytes carry out over 500 intricate metabolic functions

Liver Metabolism

37

• The liver produces cholesterol:

– At a basal level of cholesterol regardless of

dietary intake

– Via a negative feedback loop involving serum

cholesterol levels

– In response to saturated fatty acids

Plasma Cholesterol Levels

38

• Stress, cigarette smoking, and coffee drinking

increase LDL levels

• Aerobic exercise increases HDL levels

• Body shape is correlated with cholesterol levels

– Fat carried on the upper body is correlated

with high cholesterol levels

– Fat carried on the hips and thighs is

correlated with lower levels

Non-Dietary Factors Affecting Cholesterol

39

• Bond energy released from catabolized food must equal

the total energy output

• Energy intake – equal to the energy liberated during the

oxidation of food

• Energy output includes the energy:

– Immediately lost as heat (about 60% of the total)

– Used to do work (driven by ATP)

– Stored in the form of fat and glycogen

Body Energy Balance

40

• Nearly all energy derived from food is eventually

converted to heat

• Cells cannot use this energy to do work, but the

heat:

– Warms the tissues and blood

– Helps maintain the homeostatic body

temperature

– Allows metabolic reactions to occur efficiently

Body Energy Balance

41

Feeding behavior and hunger depend on one or more of

five factors

◦ Neural signals from the digestive tract

◦ Bloodborne signals related to the body energy stores

◦ Hormones, body temperature, and psychological

factors

When energy intake and energy outflow are balanced,

body weight remains stable

The hypothalamus releases peptides that influence

feeding behavior

Feeding Behaviors

42

• Glucagon and epinephrine stimulate hunger

• Insulin and cholecystokinin depress hunger

• Increased body temperature may inhibit eating

behavior

• Psychological factors that have little to do with

caloric balance can also influence eating behaviors

Hormones, Temperature, Psychological Factors

43

• Rate of energy output (expressed per hour)

equal to the total heat produced by:

– All the chemical reactions in the body

– The mechanical work of the body

• Measured directly with a calorimeter or indirectly

with a respirometer

Metabolic Rate

44

• Basal metabolic rate (BMR)

– Reflects the energy the body needs to

perform its most essential activities

• Total metabolic rate (TMR)

– Total rate of kilocalorie consumption to fuel all

ongoing activities

Metabolic Rate

45

• Body temperature – balance between heat production and heat loss

• At rest, the liver, heart, brain, and endocrine organs account for most heat production

• During vigorous exercise, heat production from skeletal muscles can increase 30–40 times

• Normal body temperature is 36.2C (98.2F); optimal enzyme activity occurs at this temperature

• Temperature spikes above this range denature proteins and depress neurons

Regulation of Body Temperature

46

Regulation of Body Temperature

Figure 24.25 47

• Organs in the core (within the skull, thoracic, and

abdominal cavities) have the highest temperature

• The shell, essentially the skin, has the lowest

temperature

• Blood serves as the major agent of heat transfer

between the core and shell

• Core temperature remains relatively constant, while shell

temperature fluctuates substantially (20C–40C)

Core and Shell Temperature

48

• The body uses four mechanisms of heat exchange

– Radiation – loss of heat in the form of infrared rays

– Conduction – transfer of heat by direct contact

– Convection – transfer of heat to the surrounding air

– Evaporation – heat loss due to the evaporation of water from the lungs, mouth mucosa, and skin (insensible heat loss)

• Evaporative heat loss becomes sensible when body temperature rises and sweating produces increased water for vaporization

Mechanisms of Heat Exchange

49

• The main thermoregulation center is the

hypothalamus

• The heat-loss and heat-promoting centers

comprise the thermoregulatory centers

• The hypothalamus:

– Receives input from thermoreceptors in the

skin and core

– Responds by initiating appropriate heat-loss

and heat-promoting activities

Role of the Hypothalamus

50

• Surface area, age, gender, stress, and

hormones

• As the ratio of surface area to volume increases,

BMR increases

• Males have a disproportionately high BMR

• Stress increases BMR

Factors that Influence BMR

51

• Low external temperature or low temperature of

circulating blood activates heat-promoting

centers of the hypothalamus to cause:

– Vasoconstriction of cutaneous blood vessels

– Increased metabolic rate

– Shivering

Heat-Promoting Mechanisms

52

• When the core temperature rises, the heat-loss center is

activated to cause:

– Vasodilation of cutaneous blood vessels

– Enhanced sweating

• Voluntary measures commonly taken to reduce body

heat include:

– Reducing activity and seeking a cooler environment

– Wearing light-colored and loose-fitting clothing

Heat-Loss Mechanisms

53

• Normal heat loss processes become ineffective

and elevated body temperatures depress the

hypothalamus

• This sets up a positive-feedback mechanism,

sharply increasing body temperature and

metabolic rate

• This condition, called heat stroke, can be fatal if

not corrected

Hyperthermia

54

• Heat-associated collapse after vigorous

exercise, evidenced by elevated body

temperature, mental confusion, and fainting

• Due to dehydration and low blood pressure

• Heat-loss mechanisms are fully functional

• Can progress to heat stroke if the body is not

cooled and rehydrated

Heat Exhaustion

55

Controlled hyperthermia, often a result of infection,

cancer, allergic reactions, or central nervous system

injuries

White blood cells, injured tissue cells, and macrophages

release pyrogens that act on the hypothalamus, causing

the release of prostaglandins

Prostaglandins reset the hypothalamic thermostat

The higher set point is maintained until the natural body

defenses reverse the disease process

Fever

56

• Good nutrition is essential in utero as well as throughout

life

• Lack of proteins needed for fetal growth and in the first

three years of life can lead to mental deficits and

learning disorders

• With the exception of insulin-dependent diabetes

mellitus, children free of genetic disorders rarely exhibit

metabolic problems

• In later years, non-insulin-dependent diabetes mellitus

becomes a major problem

Developmental Aspects

57